1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile.
2. Discussion of the Related Art
FIG. 1 illustrates a printer 1 that is an example of a conventional image forming apparatus in which an electrophotographic system is used. An optical device 20 irradiates an image forming device 10Y, 10C, 10M and 10K with light, the image forming device 10Y, 10C, 10M and 10K forms a toner image, and a transfer unit 30 conveys and transfers the toner image to a sheet material P. On the other hand, a paper feed roller 41 picks up the sheet material P stacked on a sheet material supplying device 40, the sheet material P is conveyed from a registration roller 42 to the transfer unit 30, and the toner image is transferred to the sheet material P. Then a fixing unit 50 heats and fixes the toner image to the sheet material P, the sheet material P is conveyed to a sheet material discharge roller 60, and the sheet material P is stacked on a sheet material stacking unit 70.
Because the fixing unit 50 heats and fixes the toner image, the inside of the fixing unit 50 may reach extremely high temperatures. Therefore, heat is transmitted from the fixing unit 50 to a periphery of the fixing unit 50, particularly in the transfer unit 30 or a toner storage device 80, which causes a risk of melting toner.
The sheet material P on which the toner image is fixed by the fixing unit 50 also may reach high temperatures, and the sheet material P emits the heat between the fixing unit 50 and the sheet material discharge roller 60. The heat increases temperatures of electric components, such as a sensor 90, which are provided in a conveying path between the fixing unit 50 and the sheet material discharge roller 60. When the temperature of the electric component exceeds an allowable temperature, a trouble is possibly caused in the electric component. When the sheet material P is stacked at a high temperature on the sheet material stacking unit 70 while insufficiently cooled, the toner on the sheet material P stacked on the sheet material stacking unit 70 is possibly melted to cause a trouble in that the sheet materials P adhere to each other.
Recently demands for downsizing of the machine and improvement of productivity rise in the market, and cooling of the fixing and the thermally-fixed sheet material become a large issue.
Therefore, various countermeasures against the issue have been proposed to cool the fixing and the thermally-fixed sheet material. For example, in an image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2003-307996, exhaust heat units are provided near a fixing unit and a discharge and stacking unit, and ventilation holes are respectively made between the fixing unit and the exhaust heat unit and between the discharge and stacking unit and the exhaust heat unit, thereby cooling a sheet material and a path between the fixing unit and the discharge and stacking unit.
In an image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2005-10767, a cooling fan is disposed opposite a discharge conveying path in order to generate a flow from an image forming unit side toward a discharge conveying path, and outlets are provided in the discharge conveying path opposite the cooling fan and a sidewall, thereby cooling a sheet material after fixing.
In an image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2002-333814, a duct is provided in a cooling fan provided in the apparatus in order to guide air to a paper discharge unit, and the outlet of the duct is opened immediately after a sheet exit, which allows a sheet discharged from a paper discharge port to be directly cooled after fixing.
In an image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2005-258318, an intake is provided along a recording material conveying path in an outer frame in an opposite direction to a heating unit that heats an image, an outlet and exhaust fan are provided in an outer frame on the heating side, and an intake fan is provided in an air flow path between the intake and the outlet, in a midpoint of the heating unit on the air flow path and the outlet, and in a central portion in a lengthwise direction of the heating unit. Therefore, the periphery of a fixing unit and a recording material after fixing are cooled.
In the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2003-307996, exhaust heat units are provided near the fixing unit and the discharge and stacking unit, a ventilation hole is made between the discharge and stacking unit and the exhaust heat unit. When the sheet materials are gradually stacked on the discharge and stacking unit, the ventilation hole is gradually closed to stop wind flow. Even if the ventilation hole is not completely closed, the sheet materials stacked on the discharge and stacking unit become high temperature because of the sheet material heated and fixed by the fixing unit. Therefore, the heat of the sheet material is taken in the machine, and possibly a cooling effect is insufficiently exerted.
In the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2005-10767, the cooling fan is provided in a region from the fixing unit to the outlet, and an air flow blows the sheet material after the fixing by the cooling fan, thereby cooling the sheet material. The cooling fan is disposed in the apparatus while facing a discharge conveying path, whereby the heat emitted from the fixing unit is blocked so as not be transmitted to the periphery of the fixing unit. However, because the cooling fan is disposed in the apparatus, a pressure loss is increased, and it is necessary to enlarge the fan in order to obtain a predetermined air volume, which possibly influence the machine size. Particularly, in the high-productivity machine, a lack of air volume is probably generated only by the cooling fan provided in the apparatus.
In the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2002-333814, the duct is provided in the cooling fan provided in the apparatus in order to guide the air to the paper discharge unit, and the outlet of the duct is opened immediately after the sheet exits, so that the sheet discharged from a paper discharge port can directly be cooled. Therefore, the sheet after the fixing is sufficiently cooled. However, except for the sheet after the fixing, particularly the electric component located in the conveying path from the fixing unit to the paper discharge port or the periphery of the fixing unit is insufficiently cooled.
In the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2005-258318, an air flow path is ensured along the conveying path, and the intake and the outlet are provided in the end portion, that is, in the outer frame of the apparatus, and the exhaust fan is provided in the outlet or the intake fan is provided in the air flow path, thereby cooling the periphery of the fixing unit and the sheet material after fixing. However, the air flow path is ensured along the conveying path, and the cooling fan is provided in the air flow path. Therefore, it is necessary to largely ensure the air flow path, which advantageously enlarge the machine.